Abstract
In this work, the hysteresis of elastomer composites suitable for tire compounds was reduced by using CB functionalized with pyrrole compounds containing sulfur-based functional groups reactive with the elastomer chains. CB was functionalized with bio-based pyrrole compounds: 2-(2,5-dimethyl-1H-pyrrol-1-yl)ethane-1-thiol (SHP) and 1,2-bis(2-(2,5-dimethyl-1H-pyr-rol-1-yl)ethyl)disulfide (SSP), bearing an -SH and an -SS- functional group, respectively. SHP and SSP were synthesized via a one-pot two-step synthesis, with yields higher than 70%, starting from biosourced chemicals as follows: 2,5-hexanedione from 2,5-dimethylfuran, cysteine and cysteamine. The functionalization of CB was carried out by mixing the CB with PyC and heating, with quantitative yields ranging from 92 to 97%. Thus, the whole functionalization process was characterized by a high carbon efficiency. The formation of the covalent bond between SHP, SSP and CB, in line with the prior art of such a functionalization technology, was proven by means of extraction and TGA analyses. The reactivity of the sulfur-based functional groups with unsaturated polymer chains was demonstrated by using squalene as the model compound. Poly(styrene-co-butadiene) from solution anionic polymerization and poly(1,4-cis-isoprene) from Hevea Brasiliensis were the elastomers employed for the preparation of the composites, which were crosslinked with a sulfur-based system. Pristine CB was partially replaced with CB/SHP (33%) and CB/SSP (33% and 66%). The PyC resulted in better curing efficiency, an increase in the dynamic rigidity of approximately 20% and a reduction in the hysteresis of approximately 10% at 70 °C, as well as similar/better ultimate tensile properties. The best results were achieved with a 66% replacement of CB with CB/SSP. This new family of reactive carbon blacks paves the way for a new generation of 'green tires', reinforced by a CB reactive with the polymer chains, which provides high mechanical properties and low rolling resistance. Such a reactive CB eliminates the use of silica, and thus the ethanol emission resulting from the condensation of silane is used as a coupling agent. In addition, CB-based tires are characterized by a higher mileage, at a moment in which the reduction in tire wear has become a primary concern.